The United States could end up cooperating with Iran to stop militant gains in Iraq, Secretary of State John Kerry suggested Monday in an interview with Yahoo!News.

But a Pentagon spokesman denied Monday that any military coordination with Iran is in the cards.

In his interview with Yahoo!News, Kerry didn't say that cooperation with Iran is under active discussion inside the administration.

"Let's see what Iran might or might not be willing to do before we start making any pronouncements," he said.

But he went on to say that the he "wouldn't rule out anything that would be constructive to providing real stability."

"I think we are open to any constructive process here that could minimize the violence, hold Iraq together -- the integrity of the country -- and eliminate the presence of outside terrorist forces that are ripping it apart," Kerry said.

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His comments are the first time such a high-ranking U.S. official has made such a public statement since militants from the Islamic State in Iraq and Syria began an offensive that has seen vast swaths of northern Iraq fall out of government hands.

Two senior U.S. officials said earlier that the Obama administration is exploring possible direct talks with Iran over the deteriorating situation in Iraq.

Deputy Secretary of State William Burns is in Vienna for nuclear talks with Iran and could hold discussions on the side about Iraq with Iranian Foreign Minister Mohammad Javad Zarif, a senior administration official said in a background briefing with reporters Monday.

In fact, the United States and Iran held "very brief discussions" about Iraq and the threat posed by ISIS on the sidelines of those negotiations, State Department spokeswoman Marie Harf told CNN's "The Situation Room with Wolf Blitzer."

"These engagements will not include military coordination or strategic determinations about Iraq's future over the heads of the Iraqi people," a senior State Department official said.

But in a signal the administration hasn't yet reached a conclusion about what to do, two administration officials said the United States wasn't interested in teaming up with Iran because the two share few mutual interests.

And Pentagon spokesman Rear Adm. John Kirby told reporters on Monday that the Defense Department isn't working on a plan to cooperate with Iran in Iraq.

"There are no plans to consult Iran on military actions inside Iraq," he said. "There is no plan to coordinate military activities."

Iran is an ally of Iraq's Shiite-led government, and a senior security official in Baghdad told CNN on Friday that the country had sent about 500 Revolutionary Guard troops to help fight the ISIS militants.

Iranian President Hassan Rouhani denied the report over the weekend, according to Iranian state television, but said he would be open to helping if asked.

Kurdish fighters hold back ISIS

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Despite their shared interest in stopping the advance of ISIS fighters in Iraq, the United States is wary of furthering Iran's already considerable influence there.

The Shiite Iranian regime is al-Maliki's closest ally in the region. And the Obama administration is concerned that appearing to team up with Iran would both alienate Iraq's Sunni minorityand worry Sunni allies of the United States in the region.

But, as the crisis spreads, officials around the globe are scrambling for any way to slow the militant advance.

ISIS, an al Qaeda splinter group, wants to establish a caliphate, or Islamic state, that would stretch from Iraq into northern Syria. The group has had substantial success in Syria battling President Bashar al-Assad's security forces.

Here's the latest:

Iraq's military strikes back; new images emerge

After days of violent ISIS advances, the Iraqi air force destroyed a convoy of 15 vehicles carrying ISIS fighters headed to Baiji from Mosul, Iraqi state TV reported Monday.

Separately, the air force killed more than 200 militants, state TV said. Air raids against ISIS reportedly took place in Saqlawiya, northwest of Falluja.

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ISIS moves closer to Baghdad

Iraqi army and volunteer fighters prepare in the Sedull Udeyim region of Iraq on Sunday, March 1, before an operation against ISIS in Tikrit, Iraq.

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Displaced Assyrian women who fled their homes due to ISIS attacks pray at the Ibrahim Al-Khalil Melkite Greek Catholic Church on the outskirts of Damascus, Syria, on March 1. ISIS militants recently abducted at least 220 Assyrians in Syria.

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Members of the Iraqi security forces leave Samarra, Iraq, north of Baghdad, on Saturday, February 28, to drive toward Tikrit to launch an assault against ISIS.

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A woman looks at her destroyed home after returning to the village of Al-Mansuriya, Iraq, on Saturday, February 14.

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Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on Wednesday, February 4. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was recently released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.

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A Kurdish marksman looks over a destroyed area of Kobani, Syria, on Friday, January 30, after the city had been liberated from the ISIS militant group. Kobani, also known as Ayn al-Arab, had been under assault by ISIS since mid-September.

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Smoke billows in Kirkuk, Iraq, as Kurdish Peshmerga fighters take position against ISIS militants on January 30. The aim of ISIS is to create an Islamic state across Sunni areas of Iraq and in Syria.

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Kurdish people celebrate in Suruc, Turkey, near the Turkish-Syrian border, after ISIS militants were expelled from Kobani on Tuesday, January 27.

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Collapsed buildings are seen in Kobani on January 27 after Kurdish forces took control of the town from ISIS.

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Junko Ishido, mother of Japanese journalist Kenji Goto, reacts during a news conference in Tokyo on Friday, January 23. ISIS would later kill Goto and another Japanese hostage, Haruna Yukawa.

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ISIS militants are seen through a rifle's scope during clashes with Peshmerga fighters in Mosul, Iraq, on Wednesday, January 21.

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An elderly Yazidi man arrives in Kirkuk after being released by ISIS on Saturday, January 17. The militant group released about 200 Yazidis who were held captive for five months in Iraq. Almost all of the freed prisoners were in poor health and bore signs of abuse and neglect, Kurdish officials said.

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Smoke billows behind an ISIS sign during an Iraqi military operation to regain control of the town of Sadiyah, about 95 kilometers (60 miles) north of Baghdad, on Tuesday, November 25.

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Fighters from the Free Syrian Army and the Kurdish People's Protection Units join forces to fight ISIS in Kobani on Wednesday, November 19.

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A picture taken from Turkey shows smoke rising after ISIS militants fired mortar shells toward an area controlled by Syrian Kurdish fighters near Kobani on Monday, November 3.

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Iraqi special forces search a house in Jurf al-Sakhar, Iraq, on Thursday, October 30, after retaking the area from ISIS.

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ISIS militants stand near the site of an airstrike near the Turkey-Syria border on Thursday, October 23. The United States and several Arab nations have been bombing ISIS targets in Syria to take out the militant group's ability to command, train and resupply its fighters.

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Kurdish fighters walk to positions as they combat ISIS forces in Kobani on Sunday, October 19.

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A U.S. Air Force plane flies above Kobani on Saturday, October 18.

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Heavy smoke rises in Kobani following an airstrike by the U.S.-led coalition on October 18.

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Cundi Minaz, a female Kurdish fighter, is buried in a cemetery in the southeastern Turkish town of Suruc on Tuesday, October 14. Minaz was reportedly killed during clashes with ISIS militants in nearby Kobani.

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Turkish police officers secure a basketball stadium in Suruc on October 14. Some Syrian Kurds were held there after crossing from Syria into Turkey. Tens of thousands of people fled Kobani to escape ISIS.

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Kiymet Ergun, a Syrian Kurd, celebrates in Mursitpinar, Turkey, after an airstrike by the U.S.-led coalition in Kobani on Monday, October 13.

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Alleged ISIS militants stand next to an ISIS flag atop a hill in Kobani on Monday, October 6.

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In this photo released by the U.S. Air Force on Saturday, October 4, a U.S. Navy jet is refueled in Iraqi airspace after conducting an airstrike against ISIS militants.

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A Kurdish Peshmerga soldier who was wounded in a battle with ISIS is wheeled to the Zakho Emergency Hospital in Duhuk, Iraq, on Tuesday, September 30.

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Syrian Kurds wait near a border crossing in Suruc as they wait to return to their homes in Kobani on Sunday, September 28.

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Tomahawk missiles, intended for ISIS targets in Syria, fly above the Persian Gulf after being fired by the USS Philippine Sea in this image released by the U.S. Navy on Tuesday, September 23.

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Turkish Kurds clash with Turkish security forces during a protest near Suruc on Monday, September 22. According to Time magazine, the protests were over Turkey's temporary decision to close the border with Syria.

Kurdish Peshmerga fighters fire at ISIS militant positions from their position on the top of Mount Zardak, east of Mosul, Iraq, on Tuesday, September 9.

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Iraqi volunteer fighters celebrate breaking the Amerli siege on Monday, September 1. ISIS militants had surrounded Amerli, 70 miles north of Baquba, Iraq, since mid-June.

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Kurdish Peshmerga forces stand guard at their position in the Omar Khaled village west of Mosul on Sunday, August 24.

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Kurdish Peshmergas fight to regain control of the town of Celavle, in Iraq's Diyala province, on August 24.

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Peshmerga fighters stand guard at Mosul Dam in northern Iraq on Thursday, August 21. With the help of U.S. military airstrikes, Kurdish and Iraqi forces retook the dam from ISIS militants on August 18. A breach of the dam would have been catastrophic for millions of Iraqis who live downstream from it.

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Displaced Iraqis receive clothes from a charity at a refugee camp near Feeshkhabour, Iraq, on Tuesday, August 19.

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Peshmerga fighters inspect the remains of a car that reportedly belonged to ISIS militants and was targeted by a U.S. airstrike in the village of Baqufa, north of Mosul, on August 18.

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Kurdish Peshmerga fighters fire at ISIS in Khazair, Iraq, on Thursday, August 14.

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Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and some other Yazidi people are flown to safety Monday, August 11, after a dramatic rescue operation at Iraq's Mount Sinjar. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. But only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.

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Thousands of Yazidis are escorted to safety by Kurdish Peshmerga forces and a People's Protection Unit in Mosul on Saturday, August 9.

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Thousands of Yazidi and Christian people flee Mosul on Wednesday, August 6, after the latest wave of ISIS advances.

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A Baiji oil refinery burns after an alleged ISIS attack in northern Selahaddin, Iraq, on Thursday, July 31.

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A Syrian rebel fighter lies on a stretcher at a makeshift hospital in Douma, Syria, on Wednesday, July 9. He was reportedly injured while fighting ISIS militants.

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Peshmerga fighters clean their weapons at a base in Tuz Khormato on June 25.

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New army recruits gather in Najaf, Iraq, on Wednesday, June 18, following a call for Iraqis to take up arms against Islamic militant fighters.

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Kurdish Peshmerga forces, along with Iraqi special forces, deploy their troops and armored vehicles outside of Kirkuk, Iraq, on June 12.

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Children stand next to a burnt vehicle during clashes between Iraqi security forces and ISIS militants in Mosul on Tuesday, June 10.

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Civilians from Mosul escape to a refugee camp near Irbil, Iraq, on June 10.

New images emerged Monday purporting to show a militant fighter interrogating and threatening to kill five captives.

And a video appears to show a man in an Iraqi military uniform after he was shot in the face. The fighter boasted on Facebook that he was proud of killing the man and said the video should be passed around to show what could happen to other Shiites.

The new images follow others apparently posted by ISIS to jihadi Internet forums appearing to show the executions of Iraqi security forces and a tweet, on what was claimed to be an ISIS account, saying its members had killed at least 1,700 Shiites.

CNN cannot independently confirm the authenticity of the images or tweets purportedly posted by ISIS.

More militant gains

The militant group racked up several victories across Iraq on Sunday.

The northwestern city of Tal Afar fell to ISIS, according to Iraqi Gen. Mohammed al-Quraishi. Many Tal Afar residents, including ethnic minority Shiite Turkmen, fled the fighting north toward Iraq's Kurdish region.

Also on Sunday, ISIS gained control of two villages in Diyala province, northeast of Baghdad.

And Iraqi security forces and suspected ISIS gunmen clashed near al-Khalis, about 18 miles (29 kilometers) from Diyala's capital of Baquba, al-Khalis police officials told CNN. Three mortar rounds landed near a recruitment center opened recently for volunteers to help the Iraqi army fight ISIS.

ISIS seized Iraq's second-largest city, Mosul, last week and has threatened to march on Baghdad, Iraq's capital and largest city.

President Obama met with the National Security Council late Monday to discuss Iraq.

He has not yet made a decision regarding a military strike against ISIS militants, a senior administration official told CNN.

The President will continue to consult with his team "in the days to come," according to a White House statement.

Obama's national security team met through the weekend, discussing the pros and cons of various options.

On Monday, multiple U.S. officials told CNN that the Obama administration is considering several military options such as unarmed surveillance flights, increased intelligence-gathering and airstrikes.

U.S. officials have said sending ground troops to Iraq isn't an option.

According to a senior military official, another option under consideration by the Obama administration is increasing the modest number of U.S. military advisers and trainers stationed at the U.S. Embassy compound in Baghdad.

But a U.S. official said last week that even airstrikes could prove futile given the lack of credible intelligence and lack of obvious targets presented by ISIS.

U.S. Sen. John McCain, who has called for airstrikes against ISIS, says approximately a dozen forward air controllers would be needed on the ground to carry out such attacks.

"You need to have people identify the targets in order to really be effective. Remember we're not talking about bombing in towns and cities. There are long stretches of that desert that they have to travel across in their vehicles with their guns on them," he told reporters Monday on Capitol Hill.

McCain also said he doesn't think Baghdad will fall to ISIS but the group could still wreak havoc in the capital.

"They can't take it. They haven't got enough troops and support. Remember it's a Shiite city. But what they can do is orchestrate bombings, assassinations, create turmoil. Shelling in different places. But I'm pretty confident that they can't take Baghdad," the senator said.

U.S. sends Marines

The United States is sending about 275 troops to Iraq to support its embassy in Baghdad, the White House said in a notification to Congress.

They will help the State Department in connection with efforts to temporarily relocate some embassy staffers to consulates in Basra and Erbil as well as to a support group in Jordan. The embassy remains open and a "substantial majority" of its presence in Iraq will remain in place, the White House said.

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Some embassy employees have been moved out of Baghdad, but most remain there, State Department spokeswoman Jen Psaki said Sunday.

Over the weekend, teams totaling some 170 U.S. personnel began arriving in Baghdad, according to Pentagon spokesman Rear Adm. John Kirby.

About 100 personnel were moved into the region to provide security, airfield management and logistics support, if needed, he said.

"The safety of personnel serving in diplomatic missions abroad is among our highest priorities. The presence of these additional forces will help enable the State Department to continue their critical diplomatic mission and work with Iraqis on challenges they are facing," Kirby said.

An amphibious assault vehicle with 550 Marines aboard was expected to enter the Persian Gulf on Monday, the Defense Department said. The Marines and their V-22 tilt-rotor aircraft could help evacuate Americans from Iraq if necessary, a U.S. defense official said.

Gas prices rise

Even though the ISIS advance hasn't had a major effect on the country's oil exports, gas prices around the world are rising.

Oil experts say the 4% price spike since June 6 -- which has taken a barrel of crude to $107 for the first time since September 2013 -- is being driven by fear that exports could be hit later this year, just as world demand peaks.